The purpose of this study was to statistically evaluate the influence of student placement at reading level by means of an informal reading inventory in one kind of elementary science materials. The materials were written at five levels of reading difficulty to better meet the reading ability spread found in the intermediate grades. The significance of student placement on achievement gain was evaluated by an analysis of variance. Groups were also equated with respect to reading level and teacher rating by an analysis of covariance. Population The materials were used in 21 fifth grade classrooms in four Oregon school districts. The classes were divided into three treatment groups which were distributed among the schools. Treatment Groups Treatment 1. Students read at one of five levels as determined by an individual informal reading inventory. Treatment 2. Students read at one of five levels as determined by a group informal reading inventory. Treatment 3. Students read at only the middle (C) level of the five levels supplied by the publishers. Hypotheses Tested (1) There is a significant difference in achievement on criterion test items among classes of fifth grade students who study material written at one or five reading levels when students are placed at respective reading level by an informal reading inventory administered by an individual having thorough training in the use of informal reading inventories. (2) There is a significant difference in achievement on criterion test items among classes of fifth grade students who study material written at one or five reading levels when students are placed at respective reading level by a group informal reading inventory administered by the classroom teacher. Results (1) Analysis of variance revealed no significant differences among the three treatment groups. The results indicate that the informal reading inventory will place students 1. 3 years lower in the materials used in this study than would the Metropolitan Reading Achievement tests. Additional research must be undertaken before it can be concluded that there is not a significant advantage in using the multi-level materials under study. The teacher effectiveness and guessing on the pretest variables need to be more adequately- controlled. Data on teacher rating indicated that teacher effectiveness was a valid area for further research.